This project will further examine and identify the mechanisms underlying the synergism of X-rays and immunity in the control of neoplastic growth in experimental mouse tumors. The standard radiobiological method of terminal dilution (TD50) will be employed to determine both degree of immunity and amount of cell killing by X-rays, and immunity in mice immunized by injections of X-ray attenuated tumor cells. A technique will be used in which tumor cells are prelabeled with 125-Iododeoxyuridine (IUdR); mice carrying such cells will be monitored by whole-body gamma counting. Loss of radioactivity from these mice represents cell death and will give information on both degree of immunity and kinetics of cell killing resulting from the interaction of X-rays and immunity. The destruction of tumor cells by adoptively transferred immune lymphocytes will be followed in vivo and effects of such lymphocytes on mouse tumor cells maintained in culture will be investigated.